The invention relates to new rubbery copolymers of ethylene, at least one other .alpha.-alkene and, one or several polyenes, and compositions possessing increased building tack on the basis of such copolymers and tackifiers.
Rubbery copolymers of ethylene, at least one other .alpha.-alkene and one or more polymers, the so called EDPM rubbers, are of industrial importance and have excellent resistance to ozone, weathering and ageing. This combination of properties allows them to be used for a wide variety of purposes. However, they possess little or no building tack, that is as recognized in the art the capacity of a surface of the uncured rubber to adhere to a surface of a similarly uncured rubber. A sufficiently high building tack level is a prerequisite in the preparation of many rubber-based articles and particularly of a multi-ply structure, such as drive belts, conveyor belts and particularly automotive tires. A sufficiently high building tack provides a lasting strong bond between the various layers of the article during the building and curing stages.
To compensate for the lack of such tack in rubbery copolymers of ethylene, at least one other .alpha.-alkene and one or more polyenes, it has hitherto been the practice to apply an adhesive to all the rubber surfaces to be contacted, whereby they may be bonded together to form a layered structure. However, such a procedure is laborious, costly and generally not desirable for processes on an industrial scale. In addition, it presents a hazard due to the flammability of most of the organic solvents used in the the adhesive systems. Further, in order to produce an acceptable adhesive the proportions of natural rubber required to produce an adhesive mixture possessing adequate tack are so large that the resulting cured product is significantly lower in its resistance to the effects of ozone and of ageing. Moreover, the physical and mechanical properties of the final cured mixtures are considerably inferior to those of the individual polymers, and effective covulcanization of the polymers comprising the admixture cannot be effected in an expedient and direct manner.
A wide variety of tackifying resins, termed in the art as "tackifiers", have been developed, for example phenol/aldehyde condensation products and condensation products of acetylene, alkylated phenol resins, such as the material available under the trademark AMBEROL ST 140 X, phenolated isoprene resins and phenolated isoprene copolymer resins. An advantage of such resins is that they can be readily homogenized in the rubbery material itself and thus need not be applied as separate layers onto the rubber surfaces. However, the proportions of such tackifiers required in practice to provide a sufficient level of tack are, in general, so large as to adversely effect the properties of the cured product, so much so that the physical properties of such cured product are deteriorated to the point that they are no longer commercially acceptable. A further factor is that in such resins, when tackifiers are used in large proportions, the tackifiers are liable to migrate to the rubber surface, a phenomenon known as exudation. Thus in rolled or calandered rubbery copolymers the excessive exudation caused by large quantitites of tackifiers results in the risk that the desired tackifying effect initially achieved is completely lost during storage and may possibly result in an adverse effect. Furthermore, using a large amount of tackifier is expensive.
This experience, as outlined above, supported by a legion of experiments with a large variety of tackifiers and rubbery ethylene copolymers, has led the person skilled in the art to believe that it is not possible by admixing tackifiers to increase the tack of rubbery ethylene copolymers high enough to result in copolymer-tackifier compositions of sufficient building tack.
The present invention is directed to new rubbery copolymers of ethylene, at least one other .alpha.-alkene and one or more polyenes. In another embodiment of the compositions are disclosed containing such rubbery copolymers of ethylene and one or more tackifiers, which compositions possess sufficient building tack to be successfully used in the manufacture of a wide variety of articles, in particular in the manufacture of drive belts, conveyor belts and particularly automotive tires. As an additional advantage compositions according to the present invention are conveniently prepared in a simple and inexpensive manner, and exhibit an insignificant degree of exudation of the tackifier that is included in the composition.